John Hlavin
Who I am
My most vivid childhood memories involve the ocean and marine wildlife: seeing my first shark while snorkelling in the Florida Keys; vacationing as a family at the beach; and spending countless hours surrounded by the myriads of fish at the National Aquarium. Growing up in a Northern Virginia suburb of Washington, D.C., meant being close enough to make trips to the coast not too difficult but still far enough away to make them special. My fascination eventually matured into a career aspiration. From the moment of that decision onward, I focused on becoming a marine biologist. Despite a stronger calling to the ocean, I chose to spend my undergraduate years at the University of Notre Dame working on freshwater ecosystems. I credit my interest in predatory fish to the muskie, pike and walleye I encountered on the pristine lakes of Michigan’s Upper Peninsula.
My first dive into marine science took the form of an assistantship to the Galapagos Science Center, where I contributed to the collection of field data for a sea turtle photo-identification project. That trip left no doubt in my mind that I had chosen the right career. I went on to finish off undergraduate studies as a NOAA Hollings Scholar working on Pacific herring eco-toxicology and graduated with my Bachelor of Science in biology.
I am now a PhD student in the University of Miami Shark Research and Conservation programme. My research focuses on the food web dynamics of South Florida’s coastal predatory guild, and my dream of working with marine predators has been fully realised. Through my continued education and training, I hope to develop the skill set I need to contribute to improved conservation of the ocean’s declining predator populations.
Where I work
My research projects are conducted in the diverse shallow-water habitats located along the coast of South Florida. These habitats include the Florida Reef Tract, mangrove shorelines and sheltered estuaries dense with sea grass, often separated by areas of unstructured sediment. Perhaps foremost among South Florida’s habitat assemblages is Biscayne Bay. Quite literally situated in the shadow of downtown Miami, Biscayne Bay’s proximity to a heavily urbanised area brings many challenges, including eutrophication, pollution and dense boating and fishing activity. Despite these challenges, the bay remains a highly productive estuarine ecosystem comprised of a mosaic of sea-grass, mangrove, macro-algal and patch reef habitats that many species rely on for food, shelter and reproduction.
Surprisingly, the focal species of this project, the Atlantic guitarfish Pseudobatos lentiginosus, is seldom encountered in Biscayne Bay as it prefers the more exposed shorelines of the Atlantic. This project hopes to interpret that preference through the lens of the ecological drivers of the guitarfish’s habitat choices. In that way, South Florida presents a unique opportunity to study this species not only in the ecological context of the diversity of habitats available, but also in the context of the palpable human presence that may influence distribution, habitat selection and abundance of prey resources.
What I do
An ecosystem is a delicate web of interdependent relationships between species in perpetual fluctuation at the mercy of environmental and anthropogenic factors. Trophic ecology research is thus an integral part of ecosystem-based management and species conservation. Target species cannot be properly conserved and managed without also conserving the habitats and prey resources they rely on and understanding the influence of top-down control like predation or fishing pressure.
That dependence of conservation and management on trophic ecology is what motivates my research on South Florida’s predatory fish guild, which includes a range of shark, ray and bony fish species. In addition, my research places special emphasis on intermediate predators and their importance to our coastal ecosystems. Whereas apex predators cap the very top of the food chain and are often charismatic species receiving the most scientific and media limelight, intermediate predators can fall anywhere below that apex spot, filling numerous trophic roles in the ecosystem and yet receiving considerably less attention.
The Atlantic guitarfish is the perfect example of an understudied intermediate predator silently suffering human-driven population declines in the shadows. This project will shed light on this species to aid its conservation by investigating its role, habitat and dietary resources in South Florida’s ecosystems. Sampling for this project requires capturing wild guitarfish by free-diving with cast nets. Captured individuals will undergo a swift work-up, which includes gently inducing regurgitation of dietary items, a small muscle biopsy and a cloacal swab. With these samples, a combination of stomach content analysis, faecal DNA meta-barcoding and stable isotopes will paint a highly detailed picture of the trophic ecology of the Atlantic guitarfish. By bringing attention to the resources and habitats necessary to support flourishing guitarfish populations, this project will inform conservation of an at-risk species and ecosystem-wide management of the highly impacted South Florida coast.